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Two approaches help identify cardiac surgery patients at risk for postoperative kidney failure

Research Activities, July 2011, No. 371

After coronary artery bypass grafting (CABG), between 5 and 30 percent of patients may experience acute kidney injury, defined as a rapid loss of kidney function. Once an acute kidney injury develops, there is an increased risk for poor outcomes, such as a threefold increase in 30-day mortality rates. Two criteria methods are used to define the type of acute kidney injury and its consequences. A recent study found that both sets of criteria were accurate as early predictors of mortality from acute kidney injury among CABG patients after surgery.

The Northern New England Cardiovascular Disease Study Group collected data on 24,747 consecutive patients undergoing CABG at 8 medical centers in the New England area. Patients already receiving kidney dialysis were excluded from the study. Serum creatinine levels, specifically the last preoperative and the highest postoperative readings, were used as part of both criteria methods to determine the presence of acute kidney injury and to calculate mortality risk. The two methods used were the Risk, Injury, Failure, Loss, and End-Stage Kidney Disease (RIFLE) criteria and the Acute Kidney Injury Network (AKIN) criteria, both consensus-based.

Based on the AKIN criteria, acute kidney injury was present in 30 percent of patients. The RIFLE criteria yielded similar results (31 percent). Both methods were accurate at predicting mortality rates. For example, patients with stage 3 acute kidney injury had a predicted mortality rate of 36.8 percent under AKIN and 36.4 percent under RIFLE. The risk of mortality increased in patients with a greater degree of acute kidney injury regardless of the criteria used.

The researchers recommend that providers use either criteria method to identify early in the process, patients at increased risk of declining kidney function after CABG surgery. The study was supported in part by the Agency for Healthcare Research and Quality (HS18443).